1. Field of the Invention
This invention concerns highly active insecticidal compositions comprising propetamphos and hydroprene. The novel compositions are useful for control of cockroach populations and/or for prophylactic protection against cockroach infestation.
The current invention is also directed to a process for control of cockroach population which process comprises applying to a locus of the cockroach population, in an effective cockroach population controlling aggregate amount, (a) hydroprene [an insect growth regulator (IGR)], and (b) propetamphos (an insecticide).
2. Background
The cockroach is one of the most difficult insects to control. It is primarily a nocturnal insect which forages in exposed locations at night and finds hidden harborages during the day. The life cycle of the cockroach begins with eggs formed in capsules called ootheca. The eggs first hatch into Stage I nymphs which then progress over about 74 days through five more nymphal Stages II-VI to fully developed adult cockroaches. In her adult life span, the female adult cockroach lives for approximately 144 days and produces six ootheca containing about 40 eggs each. Thus the population growth potential is tremendous. A cockroach population continues to grow in a geometrical fashion as long as the three basic requirements of food, water and harborage are sufficient. Oftentimes, a cockroach population will be found to have stabilized in number because of some limitation in one or more of the three basic requirements.
There are two possible ways to deal with the cockroach infestation. One is to submit the cockroach population to a repeated treatment with insecticide. The second is to submit it to a repeated treatment with IGR which will interfere with cockroach maturation and fertility.
It has been observed that if a stabilized cockroach population is under stress, for example when it is temporarily stressed by application of an insecticide, and the stress is ended (e.g., according to the residual activity of the insecticide), the cockroach population responds to the end of the stress by producing increased numbers of young cockroaches much beyond the previously stabilized population level. After the residual activity of the insecticide has become ineffective, the cockroach population compensates for loss due to the stress. Such compensation results in an overall population explosion, reaching much higher numbers of cockroaches than the previously stabilized population level. The population explosion occurs whenever the insecticide looses its toxic effect on the cockroaches. That is particularly true in cases when the insecticide does not affect or interfere with the reproductive potential of surviving cockroaches.
The application of insecticide alone thus has an immediate but short-term effect on reducing the cockroach population. Moreover, because the stress on the population is only temporary, eventually such application results in increased cockroach population only a short time after the insecticide residual activity ends. The residual activity of an insecticide effective on a cockroach population generally does not last for more than about eight weeks. In addition, because of the high toxicity of insecticides, it is often necessary and preferable to restrict the number of applications and the areas to which the insecticide is applied to prevent a health hazard to people.
An alternative to treatment with insecticides is to treat the infested area with environmentally safe hydroprene or other IGRs. The drawback of treatment with hydroprene or the other IGRs is the long time period before the effect on cockroaches is observed. Such delay is caused by the IGRs' mode of action. When an IGR is applied to the locus of cockroach infestation the adult cockroaches are not affected at all and the immature nymphs seemingly continue to develop through successive stages to adults. However, if the cockroaches during their nymphal development come into contact with an IGR they become irreversibly morphologically deformed and physiologically unable to reproduce. This effect, together with the excellent residual activity of IGRs, greatly impacts the cockroach population as the viable reproducing individuals begin to decline in number around four to six months after the first application of IGR to the locus of the population. In addition, although unable to reproduce, the cockroaches treated with an IGR develop into adults and compete with other cockroaches for food, water and harborage, thereby further suppressing the cockroach population.
A scaled-up test in a 1000 cubic foot testing chamber simulating a kitchen with a fairly heavy German cockroach infestation has shown that a single application of a 1.2% hydroprene fogger at 250 ml per 100 m.sup.2 provides some degree of supression of the cockroach population. However, the complete eradication of cockroaches was never accomplished.
The results obtained in scale-up tests led to a field testing of hydroprene alone or in combination with certain insecticides in actual homes and apartments with current cockroach infestations. Insecticides chosen to test the effect of such a combination on reduction of a cockroach population were DDVP, chlorpyrifos, propoxur and propetamphos. A single application of hydroprene foggers used in conjunction with DDVP or propoxur foggers provided reasonably good control but never complete eradication of the cockroach population in four single family houses and twenty-five apartments. Similarly, the hydroprene treatment alone had shown a definite hydroprene effect, i.e. the presence of anomalous nymph stages, but significant reduction of the cockroach population was never achieved within a four-month testing period.
These trials show that neither the hydroprene alone or any one of the tested insecticides alone was able to achieve safe, fast, complete and long-lasting control of cockroaches. To achieve the above goal, an insecticide was needed which in combination with hydroprene would enhance the morphogenetic action of hydroprene and complement it with its own effect.